You can find an extensive dictionary of mathematics terms on Mathwords.com. Mathwords.com breaks mathematics down into several large areas, such as arithmetic, algebra, trigonometry, and calculus. Each area is further divided into several subsections based on its particular aspects. Mathwords.com lists entries in alphabetical order and alphabetizes Greek letters using their Latinized translations while also including the original Greek letters for clarity.
While many of the entries on Mathwords.com are only definitions of mathematical terms, several terms give a brief overview and explanation of the concepts that define the words. Some entry pages have links to mathematical topics relevant to the current entry. For example, the entry defining "arithmetic mean" provides links to other key characteristics of number sets such as median and mode.
Many of these links are very helpful for mathematics students learning new subjects. For instance, in the calculus section, the main entry for the term "derivative" gives both a plain language and mathematically rigorous definition of what a derivative is, but it does not give the student any real idea of how to solve one of these problems. However, a link at the bottom of the derivative entry directs users to the page concerning all of the derivative rules, with tools valuable not only for differential calculus but also essential when students move on to integrals.